The present invention relates to a new and improved apparatus or arrangement for applying a substantially strip-shaped powder layer onto a weld seam of a can body or container, such as food cans and the like.
Apparatuses or arrangements of the above-mentioned general type are known in the art. Swiss Pat. No. 603,249 discloses a powder coating arrangement in which a stream of powder/air mixture is brought into a chamber which is open toward the weld seam and braked in the chamber by inserts located transverse to the direction of the stream which is distributed and deflected to the outlet opening. The powder particles which forcibly adhere to the deflecting plates must be removed with an additional stream from the spray chamber and blown to the weld seam. In the sense of flow technique the arrangement has many deficiencies and thereby it possesses a high consumption of transport and suction air, as well as reprocessed powder. With failing of one container or can, the whole powder cloud must be aspirated through a suction hood provided above the arrangement.
Another powder applying arrangement is disclosed in the U.S. Pat. No. 4,215,648, granted Aug. 5, 1980. In this arrangement powder is separated from the carrier gas by centrifugal separation and supplied in a tight stream at an acute angle to a spot to be coated. The powder stream is blown to the weld seam with an air cushion, for example through a porous wall of the spray chamber. In this arrangement the whole quantity of powder which has not adhered to the weld seam must be aspirated between the successive containers by outward suction. Then the powder particles are pulled because of the negative pressure formed there, inwardly of the container or can in all regions which communicate with the surroundings and deposited at locations which need not be coated, for example on the outer side or surface of the container. In addition to a great consumption of powder and energy for pressure and suction air, it is impossible to provide a small coating extending along the weld seam and having a constant thickness, since there is no possibility of dosing the powder quantity to be applied.
U.S. Pat. Nos. 4,212,266, granted July 15, 1980, and 4,205,621, granted June 3, 1980, disclose a powder applying arrangement in which the air stream supplied parallel to a powder supply conduit blows the powder from the arrangement upwardly onto the weld seam. Return of the particles which have moved upwardly but not adhered to the weld seam is performed by a collector located in the reaar part (downstream) of the arrangement. In the foregoing prior art constructions the collector or catcher communicates with the arrangement via a slot under the wall opposite to the supply and air conduits.